Numerous sensor devices are currently available for measuring the torque in either a rotating or fixed shaft or other torque transmission component. Most employ some type of strain gauged bridge mounted directly to the surface of a well defined geometric volume and aligned for maximum output. A typical example of this configuration is a solid circular shaft with four strain gauges aligned at 45.degree. to the axis of rotation.
Such strain gauged shaft sections must have some type of flange or other means for connection to the component in which the torque is to be measured. This is because this type of torque sensor device is designed to operate in series with the load it measures and all the load that normally causes the torque must go through the torque sensor. Because of that requirement, provisions must be made to allow for proper and matching bolt hole locations, keyways, and other sizing requirements in the component in which the torque is to be measured. This requirement can preclude the use of such a torque sensor in many instances. A single and relatively simple drivetrain component such as a 1 inch diameter shaft must be cut and flanged or keyed to allow for the torque sensor. In addition the torque sensor will often have a profile larger than the member it is attached to, which can create interferences with other components.
One technique being employed to overcome the difficulties of the above mentioned strain gauged, cylindrical section torque sensor is to apply strain gauges in a bridge directly to the member in which the torque is to be measured. Then, knowing the characteristics of the strain gauged bridge and gauge factor of the strain gauges, the strain can be determined. The strain is related to torque by geometric and material properties.
The direct mounting of strain gauges on existing operating equipment in field locations can be difficult. Mounting surfaces must be clean and smooth, and alignment of gauges is critical. In addition, curing of the epoxies or other adhesives used in the process can vary.
The main problem with field installation of directly mounted strain gauges is calibration--the measuring and relating of the electrical signal from the strain gauges to a known input covering its range of operation. All of the previously mentioned mounting problems could be tolerated to some extent if the mounted strain gauges could be accurately calibrated in their final state. While all torque sensors are always calibrated with a sensitivity and operating range criteria, it is usually impossible to accurately calibrate field installed strain gauges. Thus, the sensitivity of these gauges will be subject to a wide range of error.
It would be desirable to overcome the problems of prior art systems by providing a torque sensor which is easily calibrated and easily installed in the field on existing equipment without modification or disassembly of the equipment.